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BASIC CONCEPTS AND TERMS
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will result in a loss of the domain when the program quits. The saved domains are woolz binary
domain objects which can be externally modified by the various woolz filters and programs.
Within paint the domains are ordered in a dominance hierarchy. The effect of dominance is
that domains of higher dominance will always ”win” over domains of lower dominance with the
exception of when a domain is read in using the read-domain menu option (see Domain Menu). In
this case the domain read in is temporarily placed at the top of the dominance hierarchy.
To define or modify a domain the user selects a view-window and then uses the painting tools
to define the domain voxels. The selected view-window becomes highlighted and only one window
can be used for painting. If painting in a different view is required then the first view must be
de-selected by confirming that painting has finished in that window (right-button press). As soon
as painting in a window or plane finishes, all other view windows will be updated if they have
overlapping voxels.
Typical usage of the program is to define a domain in one plane then to move to the next
parallel plane and define the voxels for the same domain. In many cases these will have almost the
same 2D distribution therefore paint has the facility to propagate the 2D domain defined in one
planar section to the next. Propagation is user controllable and will provide warning (if requested)
if existing domains will be modified by the propagation process. This process is supported by
the auto-increment option which, if on, will automatically move the view to the next plane when
painting finishes (see Domain Menu).
Each domain appears as a coloured region overlaid on the grey-values of the reference image.
The first five colours appear as ”wash” overlays through which the grey-values can be seen. The
remaining colours (27) are solid but when deleted or temporarily ”lifted” will reveal the underlying
reference image. The number of colours is by default 10 but this can be modified by setting an
X11 resource. Practice has shown that the wash colours are the most useful because keeping
the reference image visible makes editing easier but there is a limitation to 5 because the paint
program has been designed to work on an 8-bit display. The colour of each overlay, the intensity of
the wash and the grey-level look-up table of the reference image can all be adjusted interactively
(see Colormap Dialog).
Paint allows the domain voxels to be defined within any arbitrary section view of the reference
image. This view is defined by a set of viewing-coordinates which comprise a fixed point (3D),
a viewing direction and a distance. The section through the reference image is perpendicular to
the viewing direction and at the given distance from the fixed point. These co-ordinates and
transformations are defined in the reference document. The viewing direction is defined by two
angles phi and theta which can be thought of as pitch and yaw respectively. If these angles are kept
constant then adjusting distance will display parallel planes from the reference image. Initially the
fixed point is set at 3D co-ordinate (0,0,0) but this can be reset at any time. Rotation is always
about the fixed point therefore if the user wishes to navigate by finding a point known to be in the
required section, this point can be set as the fixed point and then adjusting the viewing direction
will result in planes passing through that fixed point. A further navigation tool id provided by a
second fixed point in which case the degrees of freedom are reduced to a single angle, psi, which
defines rotation around the fixed line.
Given the viewing co-ordinates there is still ambiguity about orientation of the displayed section
on the screen. Two options have been defined (with only one currently available) which are ”walking
round the statue” and ”up is up”, These are also detailed in the reference document.